In this project the Principal Investigator describes studies on: 1) transmitter release and synaptic vesicle membrane recycling in the photoreceptor endings of the retina using electrophysiological and morphological techniques; 2) the effects of illumination on the structure of photoreceptor outer segments using rapid freezing at 4 degrees K and electron microscopy; 3) labeling functionally active synaptic endings in the mammalian retina with ultrastructural tracers; 4) connectivity of cone cells in the turtle retina.